Electrochemical capacitors also referred to as supercapacitors or ultracapacitors, with power densities (˜10 kW/kg) an order of magnitude higher than conventional secondary batteries represent an important segment of charge storage devices. In addition to the excellent energy and power densities, supercapacitors also offer advantages of very high charge-discharge rates and long cycle-life (>104 cycles compared with <103 cycles for lithium batteries) making them an attractive choice for applications ranging from high-load electric automotive solutions to photovoltaic systems for an integrated green-energy harnessing and storage application. While conventional supercapacitors comprise metallic charge collectors and amorphous-carbon enabled electrical double layer (EDL); carbon nanotubes (CNTs) have been explored as electrode materials for supercapacitors and Li-ion batteries due to their high electrical/thermal conductivity, chemical stability, low mass density and large surface area. Incorporation of the CNT network as a single-layer current collector and active material has lead to a light-weight, flexible charge storage device that also offers the opportunity for a roll-to-roll printing process. This ‘printed power’ solution now addresses a critical gap in the deployment of printed electronics with printed supercapacitors potentially integrated with applications such as radio frequency identification tags (RFIDs), wearable electronics, and backplanes for large-area displays amongst others.
However, it is recognized that the device internal resistance attributed to an electrode-electrolyte or inter-tube (CNT-CNT) contact resistance amongst others, may limit the power density and charge-discharge capability of supercapacitors. Known strategies to overcome this contact resistance may include coating with conducting polymers or nano structured materials including amorphous carbon.
Thus, a need exists to provide suitable electrode materials for supercapacitors and other energy charge storage devices which overcome at least some of the problems referred to above.